The long-range goal of this research is to define the physiological regulation and significance of gap junction-mediated cell-cell communication at the alveolar surface of the lung. The experimental model is focused on type II epithelial cells. In normal and injured lung, functional integrity of alveolar cells likely involves direct cell-cell communication via specialized junctional structures. Although gap junctions (GJ) are well-known in the airway epithelium, there is little information concerning formation, distribution or function of GJ in the alveolar region. GJ couple cells electrically and metabolically, via gated channels that offer low resistance to passage of electrical current or small molecules. Our preliminary data show that cultured alveolar epithelial cells selectively express GJ mRNAs and proteins, connexins, and that connexins assemble to form functional GJs. Both the pattern of connexin expression and GJ function are regulated by culture conditions and by cell-extracellular matrix interactions. The objective of this research is to define the basic features of both expression and function of gap junctions to alveolar epithelial cells. Our central hypothesis is that GJ intercellular communication (GJIC) is essential to functional integrity of the alveolar epithelium. The rationale is that definition of pathways of GJIC is essential to understanding normal alveolar cell biology, as well as the pathogenesis of lung injury and disease. The approach involves four specific aims: 1) to detail the profiles of expression and distribution of gap junction proteins, connexins, in the alveolar epithelium, and other resident cells of the peripheral lung; 2) to investigate the role of protein synthesis and turnover in regulation of connexin 43 abundance in alveolar epithelial cells; 3) to characterize pathways of connexin 43 phosphorylation and trafficking ain alveolar epithelial cells; and 4) to define the role of specific connexins and mediating GJIC between cells of the alveolar epithelium. We have established specific expertise in molecular and cell biology required to accomplish these goals. We have obtained preliminary evidence to support our hypothesis and to demonstrate feasibility of the proposed research. At completion of this research, we expect to achieve more complete understanding of regulation of GJ expression, formation and function in alveolar epithelial cells. We anticipate that these results will provide information essential to definition of mechanisms that underlie normal alveolar epithelial cell physiology, as well as the response of the lung to injury.